Jclark - it is illegal to do so - will make the gun a machinegun, even if you don't add all of the M16 parts -
even if it doesn't fire full-auto. The only M16 part you can safely use in an AR15 is the bolt carrier. At least one M16 part can't be added without machining - perhaps more, depending on what AR15 receiver is used.
Not sure why this thread from 2005 was resurrected?